after running my ac for 30 min, the two pipes going through the fire wall to the evaporator start building up brown sludge. after the ac is shut off, the sludge slowly disapears. i'm thinking its AC oil, however, usually if oil can leak, shouldn't freon leak too? i charged the AC in April when i dropped the motor in, and it still blows ice cold, and ive used the AC a lot since then.

any ideas???